Method of manufacturing electric discharge tubes



Jan. 18,- 1955 c. P. KLOPPING 2,699,981

METHOD OF MANUFACTURING ELIECTRIC'DISCHARGE TUBES Filed March 20, 1952 V II} /7 c I II: 6 V :1 1 5 .a 5 I 7 1 V :1

1 Ix k 1:" 12" u 6 v INVENTOR Curel Peter Klb'ppj ng United States Patent METHOD OF MANUFACTURING ELECTRIC DISCHARGE TUBES Carel Peter Kliipping, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application March 20, 1952, Serial No. 277,633

Claims priority, application Netherlands April 20, 1951 3 Claims. (Cl. 31623) This invention relates to methods of manufacturing electric discharge tubes for use at short wavelengths comprising plane electrodes, more particularly to the arrangement of a grid electrode and another plane electrode with the correct spacing, and it furthermore relates to tubes manufactured by the said methods.

Tubes for use at short wavelengths frequently comprise plane electrodes secured in the wall of the tube with the use of metallic discs. In this case, it is of importance that the spacings between the electrodes which, as a rule are very small, should as far as possible be the same for all tubes of the same type, in other words said spacings are required to be reproducible. In most cases in such tubes comprising plane electrodes, at first a grid electrode is secured in the tube, whereafter for example a cathode and an anode may be positioned and spaced by the correct distances from the said grid. More particularly, the spacing between cathode and grid is in this case diflicult to reproduce with accuracy, said spacing requiring to be very small. As a rule, the cathode under the microscope is moved towards the grid until the correct spacing is obtained. However, this is a time-consuming operation in which individual skill is important.

The object of the invention is to provide an improved mtethod of manufacturing such an electric discharge tu e.

According to the invention, a method of manufacturing electric discharge tube for use at short wavelengths and comprising plane electrodes, more particularly for adjusting the correct spacing between a grid electrode comprising a plurality of parallel wires with equal spacings and another plane electrode of the tube, is characterized in that the said electrodes are first brought approximately to the correct distance from one another adjusting their mutual capacity, whereafter a light beam is directed in an inclined position from the side of the grid wires onto the said electrodes, in such manner that the grid wires throw shadows on the other plane electrode, the perpendicular projection of each grid wire onto the other plane electrode exactly coinciding with the shadow of another grid wire, if the said electrodes are spaced correctly.

In order that the invention may be readily carried into effect, it will now be described in greater detail with reference to the accompanying diagrammatic drawing, showing diagrammatically a device for carrying out the method according thereto.

In the figure, the reference numeral 1 indicates the cathode of a tube for use at short wavelengths secured with the use of a cylinder 2 to a supporting member 3. The latter comprises a flange 4 in which three apertures are provided. The assembly is secured 'by means of bolts 5 and nuts 6 to a sealed-in plate 7. The nuts 6 are embraced by holders 8, which are urged by springs 9 and a bolt 10 against and about the nuts 6. The holders 8 each comprise, at their lower ends, a ribbed disc 11 capable of being turned by hand. Springs 12 are provided between the flange 4 and the disc 7, so that the flange 4 is urged against the nuts 6. Above the cathode 1, a grid 13 constituted by parallel wires is secured to a sealed-in disc 14, a hollow anode 15 being sealed-in above the grid 13.

In order that the spacing between cathode 1 and the grid 13 may be accurately adjusted, the assembly of electrodes and sealed-in discs is placed in a holder 16, the set screws 6 being tightened as evenly as possible by means of the discs 11 and the holders 8 until a measur- 2 ing device (not shown) indicates that the required grid/ cathode capacity is approximately attained. A light beam 17 falls at an angle onto the grid 13 such that, if grid 13 and cathode 1 are spaced correctly, the perpendicular projection of each grid wire is located exactly above a shadow of another grid wire. The light beam is preferably placed in an inclined position such that, if the grid and the cathode are correctly spaced, each grid wire is located above the shadow of another grid wire 3 to 4 places from said grid Wire. Since the spacing is already approximately correct due to the capacity measurement, the grid wires are already located approximately above the associated shadows, so that by further adjustment of the nuts 6 the shadows may be brought accurately under the correct grid wires. When three set screws are used it is possible to move the cathode in any desired direction. It appears that this method of adjustment is extremely secure and very accurate and that errors substantially do not occur. Furthermore, it is evident at a glance whether the grid is covered with dust particles and whether the grid is regular, that is to say that the wires extend exactly in parallel and all of them are equally spaced. If the latter is not the case, some shadows will still be seen.

After the cathode has been correctly adjusted, it may be fixed in position, for example, by welding, cementing or soldering of the nuts 6. It is advantageous to provide an amount of solder on the supporting body 3, so that the solder can flow, due to heating, between the flange 4 and the disc 7, thus fixing said parts with respect to one another.

With the use of a microscope which permits of viewing through the hollow anode 15, it may be ascertained whether the perpendicular projection of each grid wire coincides with a shadow on the surface of the cathode. Use is preferably made of a cathode having a very smooth metallic surface of which the electron-emitting layer is obtained by diffusion from the interior, since the shadows on such a smooth surface are sharply defined. It is also possible by means of the described method to bring two grids at the correct mutual distance, of which the wires are at right angles to one another.

After adjustment, the aperture in the anode is filled up, for example, by screwing-in a pin. The further finishing of the tube takes place in the usual manner.

In the case under consideration, the grid comprises wires of 12 microns diameter with spacings of 50 microns, the distance between grid and cathode being 40 microns.

A great advantage of the method described is furthermore that it is no longer necessary to measure the spacing between cathode and grid from the side through the glass wall, since glass frequently leads to incorrect adjustment due to deformation of the image.

What I claim is:

1. A method of adjusting the correct, predetermined spacing between two plane electrodes mounted in a closed but unsealed electric discharge tube in which one of said electrodes is a grid electrode having a plurality of spaced, parallel wires comprising the steps of; initially approximating the correct spacing between said two electrodes by adjusting their mutual capacity, angularly directing a light beam on the wires of said grid electrode in such a manner that the grid wires cast shadows on the surface of the other plane electrode, and the perpendicular projection of each grid wire on the other plane electrode is adapted to coincide with the shadow of another of said grid wires on said other plane electrode when said electrodes are spaced correctly.

2. A method of adjusting the correct, predetermined spacing between two plane electrodes mounted in a closed but unsealed electric discharge tube in which one of said electrodes is a grid electrode having a plurality of spaced, parallel wires comprising the steps of; initially approximating the correct spacing between said two electrodes by adjusting their mutual capacity, angularly directing a light beam on the wires of said grid electrode, and moving said other plane electrode relative to said grid electrode by an adjusting means having a plurality of adjusting screws until said grid wires cast shadows on the surface of the other plane electrode and the perpendicular projection of each grid wire on the plane electrode coincides with the shadow of another of said grid wires;

3. A method of adjusting the correct, predetermined spacing between two plane electrodes mounted in a closed but: unsealed electric; discharge tube 111:Wh10h one of said electrodes is a tgridhelectrode ha-Yinga. plurality of spaced, parallel wires comprising the steps Qf;,initially approximating the correct spacing between -saidtWo electrodes: by adjusting their mutual. capacity, angularly directing-a light beam on the wires of said grid electrode; moving said other plane electrode relativetosa'idggrid electrode by an adjusting means havinga plurality of adjusting. screws until; said grid Wires cast shadowson the surface of; the other plane electrode and the perpendicular projection of each grid wire on the plane electrode-coincideswiththeshadow of another of said-grid wires, and bonding said adjusting screws to a supporting member of said other plane electrode thereby permanently fixing said other plane electrode in said correct, predetermined position.

References. Cited in the file of this patent UNITED STATES PATENTS 2,115,866 Lux. .-,-F May 3, 1938 2,167,826 Bull Aug. 1, 1939 2,191,884 Gall et a1 Feb. 27, 1940 2,402,119 Beggs June 18, 1946 

